Bubble blowing pen cap



FIG. 1 is a front elevational view of a bubble blowing pen cap showing my new design in an exploded condition;

FIG. 2 is a front elevational view of FIG. 1 with the bubble blowing pen cap in a stored position;

FIG. 3 is a left side elevational view;

FIG. 4 is a right side elevational view; and,

FIG. 5 is a top plan view thereof.

The broken line showings of the writing instrument are for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a bubble pen cap, as shown and described. 